1. Field of the Invention
The present invention relates to a damper support, and more particularly to a damper support to be used as an engine mount.
2. Description of the Prior Art
Generally speaking, a damper support is so constructed that a rubber elastomer is interposed between one mounting fixture and the other mounting fixture. This well known damper support has a small damping factor because the loss factor of rubber is low, but is required as an engine mount to have a high damping factor in the vibrations of low frequency range (in the vicinity of 15 Hz) and to have a small dynamic spring constant in the vibrations of high frequency range (in the vicinity of 100 Hz).
In order to meet those requirements, two damper supports making use of the elasticity of rubber and the flow resistance of a fluid has been proposed by Japanese Patent Publications No. 48-36151 published on Nov. 1, 1973 and No. 52-16554 published on May 10, 1977. However, since a liquid is confined in the damper supports proposed, there are problems both in the leakage of the liquid from the adhered portions between the rubber and the fixtures and from the pin holes in the rubber and in the fatigue of the rubber due to the liquid. Moreover, it is difficult to maintain the pressure of the gas confined at a constant level for a long time. In order to maintain the gas pressure constant, it is sufficient to pump a gas at all times, as in an pneumatic spring, by the use of a compressor. The piping and wiring of the compressor are required to make the system complex and expensive thereby to raise a problem in practice.
As a damper support of the aforementioned type, moreover, there has also be proposed a U.S. Pat. No. 4,159,091 to Le Salver et al. The damper support disclosed in that U.S. Patent is so constructed that a partition wall partitioning a main confined chamber and an auxiliary confined chamber is made movable. As a result, the dynamic spring constant in a high frequency range (at 100 Hz) becomes far smaller than that of the construction, in which the partition wall is stationary, so that the U.S. Patent is more perferable than the aforementioned two Japanese Patent Publications in respect of the synamic spring constant characteristics in the high frequency range. However, not only in the vibrations of a low frequency range (in the vicinity of 15 Hz) and of a small amplitude (.+-.0.5 mm) but also in the vibrations in a high frequency range and of a small amplitude (.+-.0.05 mm), the flow of the fluid passing through a round orifice, which is formed in the partition wall, becomes turbulent even under the condition in which the flow speed through that orifice is considerably decreased. As a result, the damping factor is increased even in the high frequency range similarly to the low frequency range thereby to raise a problem that the damping characteristics in the high range are not satisfactory.